My first FAL was a Century L1a1 "Sporter", which consisted of a surplus British L1a1 parts kit, ugly thumbhole stock, and a metric Imbel receiver that was modified to accept an inch-pattern charging handle.
Since Century cut off the last inch of threaded barrel, my options for installing a flash suppressor were to either purchase a new L1a1 barrel (expensive), have a gunsmith re-thread the muzzle (still expensive), or to do something that would make Bubba proud. I chose the latter. Purchased a used L1a1 flash suppressor and some JB Weld. Yep, I epoxied it in place. Has worked great for a decade now.
Since thumbhole stocks stopped being a legal requirement, I rather hastily purchased a real L1a1 pistol grip and buttstock. Unfortunately, while in the process of installing them, I discovered that Century removed the pistol grip stud on the lower receiver.
I ended up trading the inch pattern lower receiver for a used metric one. Problem seemed to be solved.. However, it was immediately obvious that the metric rear sight was on a lower plane than the inch front sight. Though I never tried it, I suspect that it could be adjusted no better than twenty feet low at a hundred yards.
Have just recently learned that Israeli rear sights are 4mm higher than other metric rear sights, so hopefully that will fix the iron sight problem (part is still on backorder).
Anyhow, so now we have a parts gun with a metric lower and an inch upper. Ugly as all get out, due mainly to the inch pattern handguard. Solution: replace the British handguard with one of the few handguards on the market that will fit both inch and metric rifles. This ended up being a Tapco T48 style handguard (the T48 was the main competition against the M14 during the rifle trials of pre-Vietnam days).
The end result looks pretty cool. The only remaining parts from the initial purchase is the upper receiver and the barrel.
Keep in mind that if you remove the thumbhole stock from a Century L1a1 "Sporter" and put a pistol grip and flash suppressor on it, you will need to add the appropriate number of 922r compliance parts.